Natsume is a pretty good suggestion. There are some episodes that can have sad themes, but not any worse than you find in Disney movies aimed at kids. Also, there is a lot of content so you can just turn it on and let it play for a while to keep them busy. Finally, it is an anthology, so episodes are self-contained stories for the most part, so if they get distracted and miss the plot of an episode, its not really an issue.